The present invention relates generally to operation of gaseous discharge lamps. More particularly, the present invention relates to a transformerless electronic ballast for operating gaseous discharge lamps.
Ballast circuits are generally used in gaseous discharge lighting systems to regulate the supply of electrical power to the lamp. The type and size of lamp to be operated are typically determinative of how the ballast circuit will be configured. For example, high intensity discharge (HID) lamps such as mercury, metal halide, and high pressure sodium lamps are usually operated at high wattage and require a different ballast circuit than lamps such as fluorescent lamps which operate at relatively low wattage. Even among lamps of the same type (i.e., mercury, metal halide, high pressure sodium, fluorescent, etc.) the specific lamp wattage can vary, which in turn requires a corresponding variance of elements within the ballast circuit in order to optimize operation of the lamp. As a result, conventional ballast circuits are unable to accommodate proper operation of different lamp types and/or lamps of the same type which operate at different wattages.
What is needed, therefore, is a versatile ballast circuit that eliminates difficulties and disadvantages of prior art ballast circuits.
The present invention eliminates the difficulties and disadvantages of the prior art by providing an electronic ballast for operating a discharge lamp and is particularly well suited for operation of high intensity discharge lamps such as metal halide and high pressure sodium. The electronic ballast includes a filter circuit for removing noise from an electrical power signal provided by a source of electrical power, producing a filtered power signal. A power factor correction circuit adjusts the power factor of the filtered power signal and produces a corrected power signal. Included in the power factor correction circuit is a first programmable inductor circuit having a plurality of selectable inductance values for varying the amount of power factor adjustment. This programmable inductor circuit allows the power factor correction circuit to adjust the power factor as needed for operating different lamps. A power supply circuit converts electrical power received from the filtered power signal to a power level sufficient to operate the electronic ballast. An output circuit receives the corrected power signal and produces an electrical signal to ignite and operate the discharge lamp. The output circuit includes an ignition circuit for producing an oscillating voltage signal for igniting the discharge lamp, and an operating circuit for producing an oscillating current signal to operate the discharge lamp after ignition. In a preferred embodiment, the ignition circuit oscillates the voltage signal in the high frequency range of about 60 KHz to about 500 KHz. A control circuit controls the overall operation of the electronic ballast.
The control circuit may use various types of sensor feedback to control operation of the ballast circuit. For example, the ballast circuit may include a current monitor for monitoring the electrical signal provided to the discharge lamp. The current monitor signal can then be used by the control circuit to determine when the lamp is lit so that it knows when to switch from an ignition mode to an operating mode.
The ability of the ballast circuit to accommodate operation of different discharge lamps is further enhanced by including within the ignition circuit a second programmable inductor circuit having a plurality of selectable inductance values for oscillating the voltage signal at different frequencies. Additionally, the operating circuit may include a programmable resistor circuit having a plurality of resistance values for supporting operation of a plurality of different types of discharge lamps.
The control circuit preferably includes a programmable digital signal processor. The digital signal processor is programmed to control switches used in connection with the programmable inductor circuits and the programmable resistor circuit. The switches have multiple switch positions corresponding to the inductance and resistance values, and each switch is controlled by the digital signal processor to position the switches so as to optimize operation of the particular discharge lamp that is connected to the ballast circuit.
Current supplied to the discharge lamp may be controlled by power MOSFET switches in combination with opto-isolators that are controlled by the digital signal processor to boost current above that otherwise achievable by the digital signal processor alone. To reduce the potential for noise, the power MOSFET switches may be of the double gated variety.